Management zone delineation using a modified watershed algorithm

Le zonage intra-parcellaire est une méthode couramment utilisée pour gérer la variabilité intra-parcellaire. Ce concept consiste à partitionner une parcelle en zones de management selon une ou plusieurs caractéristiques du sol et/ou du couvert végétal de cette parcelle. Cet article propose une méthode de zonage originale, basée sur l'utilisation d'une méthode de segmentation d'image puissante et rapide : l'algorithme de ligne de partage des eaux. Cet algorithme d'analyse d'image a été adapté aux spécificités de l'agriculture de précision. Les performances de notre méthodes ont été testées sur des cartes biophysiques haute résolution de plusieurs champs de blé situés en Bourgogne. / Site-specific management (SSM) is a common way to manage within-field variability. This concept divides fields into site-specific management zones (SSMZ) according to one or several soil or crop characteristics. This paper proposes an original methodology for SSMZ delineation which is able to manage different kinds of crop and/or soil images using a powerful segmentation tool: the watershed algorithm. This image analysis algorithm was adapted to the specific constraints of precision agriculture. The algorithm was tested on high-resolution bio-physical images of a set of fields in France.ZONAGE;PARCELLE;TELEDETECTION;BLE;SEGMENTATION D'IMAGE;AGRICULTURE DE PRECISION;FRANCE;BOURGOGNE;PRECISION AGRICULTURE;MANAGEMENT ZONES;REMOTE SENSING;IMAGE ANALYSIS;WATERSHED SEGMENTATION

Comparing vineyard imagery acquired from Sentinel-2 and Unmanned Aerial Vehicle (UAV) platform

Aim: The recent availability of Sentinel-2 satellites has led to an increasing interest in their use in viticulture. The aim of this short communication is to determine performance and limitation of a Sentinel-2 vegetation index in precision viticulture applications, in terms of correlation and variability assessment, compared to the same vegetation index derived from an unmanned aerial vehicle (UAV). Normalised difference vegetation index (NDVI) was used as reference vegetation index.Methods and Results: UAV and Sentinel-2 vegetation indices were acquired for 30 vineyard blocks located in the south of France without inter-row grass. From the UAV imagery, the vegetation index was calculated using both a mixed pixels approach (both vine and inter-row) and from pure vine-only pixels. In addition, the vine projected area data were extracted using a support vector machine algorithm for vineyard segmentation. The vegetation index was obtained from Sentinel-2 imagery obtained at approximately the same time as the UAV imagery. The Sentinel-2 images used a mixed pixel approach as pixel size is greater than the row width. The correlation between these three layers and the Sentinel-2 derived vegetation indices were calculated, considering spatial autocorrelation correction for the significance test. The Gini coefficient was used to estimate variability detected by each sensor at the within-field scale. The effects of block border and dimension on correlations were estimated.Conclusions: The comparison between Sentinel-2 and UAV vegetation index showed an increase in correlation when border pixels were removed. Block dimensions did not affect the significance of correlation unless blocks were < 0.5 ha. Below this threshold, the correlation was non-significant in most cases. Sentinel-2 acquired data were strongly correlated with UAV-acquired data at both the field (R2 = 0.87) and sub-field scale (R2 = 0.84). In terms of variability detected, Sentinel-2 proved to be able to detect the same amount of variability as the UAV mixed pixel vegetation index.Significance and impact of the study: This study showed at which field conditions the Sentinel-2 vegetation index can be used instead of UAV-acquired images when high spatial resolution (vine-specific) management is not needed and the vineyard is characterised by no inter-row grass. This type of information may help growers to choose the most appropriate information sources to detect variability according to their vineyard characteristics

Une pratique sociale à l'épreuve de la conservation de la nature. Incertitudes et controverses environnementales autour de la dégradation de la pêche dans la Réserve de la Biosphère du Delta du Danube.

Cette thèse présente les mutations d une pratique sociale qui repose sur l interaction directe avec l environnement la pêche, dans l espace du delta du Danube, territoire doté d une remarquable richesse écologique et engagé, après 1990, dans une double transition socio-économique et écologique qui implique une redéfinition radicale des pratiques d appropriation des ressources naturelles. Caractérisée par une multiplication des acteurs, des savoirs et des actions, la création d une Réserve de Biosphère du Delta du Danube met à l épreuve l existence même de la pratique de pêche et l interaction des habitants avec les ressources désormais naturelles du delta. A travers une analyse des dispositifs de réglementation des droits de pêche expérimentés dans la Réserve au cours des 20 dernières années, cette thèse présente la dégradation de la pêche comme un espace d'incertitude où les êtres de la pêche : acteurs sociaux et poissons, sont redéfinis, expliqués, apprivoisés, mobilisés dans la définition de nouvelles formes d'interaction entre les acteurs sociaux et des ressources naturelles. Dans un contexte de persistance des pratiques de pêche illégales, les indicateurs utilisés dans la formulation des droits de pêche ont une faible capacité à faire évoluer les pratiques. L'approche développée dans cette thèse est clairement confrontée à la manière dominante de penser et de faire dans les politiques de conservation, orientées vers une plus grande rationalisation et la formulation de chaînes logiques entre des indicateurs, des droits et des résultats attendus. Nous montrons les limites de cette approche, qui devrait avoir comme préoccupation première de dépasser la distinction entre ceux qui savent et ceux qui pêchent , en facilitant l émergence des accords collectifs sur la définition des acteurs, des ressources et de leur état écologique. Nous montrons que dans le monde de la pêche artisanale, la réussite des dispositifs de gestion de la pêche dépend de leur capacité à prendre en considération les savoirs, les pratiques et les capacités critiques des acteurs locaux, développés au cours d une longue appropriation des ressources.In the last two decades, different fishing rights systems have been experimented in the Danube Delta Biosphere Reserve fisheries in order to orient natural resources exploitation practices towards the conservation of biodiversity. Overfishing is considered as one of the main threats to conservation in this ecologically fragile area, since 1989, when the communist productivist model was replaced by conservationist policies. Characterized by the multiplication of actors and knowledge production, the creation of the Biosphere Reserve of Danube Delta is challenging the continuity of fishing practices. Based on an analysis of the fishing rights systems experienced in the reserve, this work presents the degradation of fisheries as an area of uncertainty where social actors and fishing resources are redefined, explained, tamed and mobilized in the definition of new forms of ecological interactions between actors and resources. Indicators and proofs of sustainable fisheries are built on the ground, while experimenting different fishing rights systems. In a context of persisting illegal fishing practices and persistent controversies, fishing rights do not legitimate the introduction of more restrictive measures, and have a week capacity of changing practices. The approach developed in this thesis tries to go beyond the classical distinction between knowledge producers and nature users, by considering knowledge production, rights definition and social practices over nature as interconnected elements of the same process of nature appropriation. The perspective developed in this work is clearly confronted to the dominant way of thinking and doing in conservation policies, oriented towards a greater rationalization and the pre-formulation of a logical chain between measures, effects and outcomes. We show the limits of this approach, which should be primarily concerned by overcoming the distinction between "those who know" and "those who fish", facilitating the emergence of collective agreements on the definition of resources and their ecological status. We show that in the world of artisanal fisheries, the success of fisheries management incentives depends on their ability to take into account the diversity of knowledge, practices and critical capacities that local actors developed through resources appropriation practices.NANTERRE-PARIS10-Bib. élec. (920509901) / SudocSudocFranceF

Temporal stability of within-field variability of total soluble solids of grapevine under semi-arid conditions: a first step towards a spatial model

Aims: This work focuses on the study of the intra- and inter-annual Temporal Stability of Within-Field Variability (TSWFV) of Total Soluble Solids (TSS) as an estimate of grape maturity. Methods and results: The experiment was carried out between 2009 and 2015 in four fields located in the Maule Valley, Chile, under irrigated conditions. Each field corresponded to a different cultivar (namely Cabernet-Sauvignon, Chardonnay, Sauvignon blanc and Carménère), and data collection ranged over two to four years depending on the field. A regular sampling grid was designed within each field, and TSS was measured at each site of the grid on different dates (from veraison to harvest). A Kendall test (W) was used to analyse the TSWFV of TSS between all dates for each cultivar and season. A Spearman’s rank correlation coefficient (rs) was used to analyse the relationships between each sampling date and the date of harvest considered as the reference. Results of the study highlighted high within-field variability in TSS. The W test showed significant intra- and inter-annual TSWFV, and rs values showed a high and significant correlation between sampling dates. Conclusion: These results are of interest for precision viticulture since, under the conditions of the experiment, the spatial patterns of the TSS maps obtained 40 days before harvest remain the same until harvest. Therefore, early target sampling of TSS may provide a good estimate of the spatial variability of grape maturity at harvest. Significance and impact of the study: The inter-annual stability of the TSS spatial patterns makes it possible to propose a simple empirical spatial model that allows estimation of TSS values for the whole field using only one reference measurement, provided that historical data are available

Potential of Sentinel-2 satellite images to monitor vine fields grown at a territorial scale

Aim: The aim of this short note is to provide first insights into the ability of Sentinel-2 images to monitor vine growth across a whole season. It focuses on verifying the practical temporal resolution that can be reached with Sentinel-2 images, the main stages of Mediterranean vineyard development as well as potential relevant agronomic information that can be seen on the temporal vegetation curves arising from Sentinel-2 images. Methods and results: The study was carried out in 2017 in a production vineyard located in southern France, 2 km from the Mediterranean seashore. Sentinel-2 images acquired during the whole vine growing cycle were considered, i.e. between the 3rd of March 2017 and the 10th of October 2017. The images were used to compute the classical normalized difference vegetation index (NDVI). Time series of NDVI values were analyzed on four blocks chosen for exhibiting different features, e.g. age, missing plants, weeding practices. The practical time lag between two usable images was closer to 16 days than to the 10 theoretical days (with only one satellite available at the date of the experiment), i.e. near 60% of the theoretical one. Results show that it might be possible to identify i) the main steps of vine development (e.g. budburst, growth, trimming, growth stop and senescence), ii) weed management and inter-row management practices, and iii) possible reasons for significant inter-block differences in vegetative expression (e.g. young vines that have recently been planted, low-productive blocks affected by many missing vines). Conclusions: Although this experiment was conducted at a time when Sentinel-2b was not fully operational, results showed that a sufficient number of usable images was available to monitor vine development. The availability of two Sentinel satellites (2a and 2b) in upcoming seasons should increase the number of usable images and the temporal resolution of the time series. This study also showed the limitations of the Sentinel-2 images’ resolution to provide within-block information in the case of small blocks or blocks with complex borders or both. Significance and impact of the study: This technical note demonstrated the potential of Sentinel-2 images to characterize vineyard blocks’ vigor and to monitor winegrowers’ practices at a territorial (regional) scale. The impact of management operations such as weeding and trimming, along with their incidence on canopy size, were observed on the NDVI time series. Some relevant parameters (slope, maximum values) may be derived from the NDVI time series, providing new insights into the monitoring of vineyards at a large scale. These results provided areas for further investigation, especially regarding the development of new indicators to characterize block-climate relationships

How to better estimate bunch number at vineyard level?

Despite the extensive use of sampling to estimate the average number of grape bunches per vine, there is no clearly established sampling protocol that can be used as a reference when performing these estimations. Each practitioner therefore has their own sampling protocol. This study characterised the effect of differences between sampling protocols in terms of estimation errors. The goal was to identify the most efficient practices that will improve the early estimation of an important yield component: average bunch number. First, the appropriateness of including non-productive vines (i.e., dead and missing vines) in the sampling protocol was tested; the objective was to determine whether it is relevant to estimate two yield components simultaneously. Second, sampling protocols with sampling sites of varying size were compared to determine how the spatial distribution of observations and potential spatial autocorrelation affect estimation error. Third, a new confidence interval for estimation error was determined to express expected error as a percentage. It aimed at designing a new tool for finding the best sample size in an operational context. Tests were performed on two vineyards in the South of France, in which the number of bunches per vine had been exhaustively determined on all the plants before flowering. The results show that the simultaneous estimation of number of bunches and proportion of dead and missing vines increased the estimation errors by a factor of 2. Despite the low spatial autocorrelation of bunch number, the results show that the observation must be spread across at least 2 or 3 sampling sites to reduce estimation errors. Finally, the confidence intervals expressed as a percentage were validated and used to define an adequate sample size based on a compromise between the expected precision and the variability observed in the first measurements

Yield sensing technologies for perennial and annual horticultural crops: a review

Yield maps provide a detailed account of crop production and potential revenue of a farm. This level of details enables a range of possibilities from improving input management, conducting on-farm experimentation, or generating profitability map, thus creating value for farmers. While this technology is widely available for field crops such as maize, soybean and grain, few yield sensing systems exist for horticultural crops such as berries, field vegetable or orchards. Nevertheless, a wide range of techniques and technologies have been investigated as potential means of sensing crop yield for horticultural crops. This paper reviews yield monitoring approaches that can be divided into proximal, either direct or indirect, and remote measurement principles. It reviews remote sensing as a way to estimate and forecast yield prior to harvest. For each approach, basic principles are explained as well as examples of application in horticultural crops and success rate. The different approaches provide whether a deterministic (direct measurement of weight for instance) or an empirical (capacitance measurements correlated to weight for instance) result, which may impact transferability. The discussion also covers the level of precision required for different tasks and the trend and future perspectives. This review demonstrated the need for more commercial solutions to map yield of horticultural crops. It also showed that several approaches have demonstrated high success rate and that combining technologies may be the best way to provide enough accuracy and robustness for future commercial systems